1. Goa: Goa is a coastal state, and summers aren't very comfortable here.
2. Rajasthan: It gets difficult to explore the forts and palaces under the scorching heat of the summer months.
3. Varanasi: The cool weather months are the best to explore Varanasi.
4. Rishikesh: It gets huge crowds during the time of Char Dham Yatra.
5. Kerala: The beachside of Kerala gets hotter in summer.
6. Kolkata: Kolkata is extremely humid during the summer.
7. Darjeeling: The hill station gets overcrowded during the summer months.
These destinations either get too hot or too humid during summers or get overpacked with tourists.
Travelling in extremely hot weather might make you sick.
And in overcrowded places, you might face traffic issues and also it gets hard to get good hotel rooms.